Optimized cooperation between resource list servers and presence servers

ABSTRACT

A method, system and computer program product for optimized cooperation between resource list servers and presence servers. The method including receiving a subscription request from a watcher, where the subscription request identifies a resource list and is a request to receive presence information regarding each of a plurality of presentities listed on the resource list, and generating a subscription request to a presence server for presence information regarding any presentity listed on the resource list only if no other currently-active subscription request is known by the resource list server to exist for presence information regarding the presentity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/633,690, entitled “Optimized Cooperation Between Resource ListServers and Presence Servers” and filed Dec. 8, 2009, the disclosure ofwhich is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to computer networks in general, and moreparticularly to providing information to networked entities regardingthe status of other networked entities.

BACKGROUND OF THE INVENTION

The Session Initiation Protocol (SIP) is a protocol for creating,modifying, and terminating computer network-based communicationsessions, such as for an Internet-based telephone call between two ormore participants. Since its introduction numerous enhancements to SIPhave been proposed, including the SIP Instant Messaging and PresenceLeveraging Extensions (SIMPLE) framework in which one or more networkentities, such as computer users, create subscriptions on a server,known as a “presence” server, to receive presence information regardinganother network entity, referred to as a “presentity.” When a change inthe presentity's presence information is detected, such as when thepresentity “publishes” such a change to the presence server, SIP is usedto send a notification to the subscribers regarding the change.

Further enhancements to SIP, such as those described in RFCs 3857 and3858 of the Internet Engineering Task Force, provide a mechanism forsubscribing to information regarding subscribers to a presentity'spresence information. In this context, subscribers to a presentity'spresence information are referred to as “watchers,” the informationregarding these subscribers is referred to as “watcher information,” andthe subscriber to watcher information is referred to as a “watcherinformation subscriber.” Both presence information and watcherinformation are preferably maintained in the Extensible Markup Language(XML). The watcher information subscriber may use this information, forexample, to detect unauthorized subscriptions for the presentity'spresence information.

Other enhancements to SIP, such as those described in RFCs 3265 and4662, provide a mechanism for enabling a watcher to subscribe to receivepresence information for a group of presentities, whereby the watchersends a single subscription request to a resource list server withrespect to a resource list that includes multiple presentities. Then,for each presentity listed in the resource list, the resource listserver sends a separate subscription request on behalf of the watcher toa presence server that will provide presence information for thatpresentity. For each watcher subscription that is made to the sameresource list, the resource list server generates separate presenceserver subscriptions for each presentity on the list. Similarly, forwatcher subscriptions to different resource lists that include the samepresentity, the resource list server generates multiple presence serversubscriptions for the same presentity. The management of eachsubscription necessarily requires computer processing, storage, andnetworking resources.

In the prior art a system is provided for maintaining presenceinformation of public group members, which includes a presence serverand a group list management server, and further includes a presencegroup server connected to the presence server and the group listmanagement server and adapted to obtain information of the public groupmembers from the group list management server according to a receivedsubscription request for the presence information of the public groupmembers, subscribe for the presence information of the public groupmembers from the presence server, and save the presence information ofthe public group members. A presence group server and a method formaintaining presence information of public group members are alsoprovided. In this system, unfortunately, multiple requests for thepresence information of the public group members result in multiplesubscriptions being created for each member of the group.

The prior art also describes using routing to distribute SIP requestsamong clusters, where a number of different presence server clusters aredeployed, each cluster handling incoming SIP requests for a particularsubset of users. In this scenario a separate resource list servercomponent is deployed to handle all subscriptions on presence lists.Unfortunately, here too are multiple subscriptions generated formultiple requests for presence information regarding the samepresentity.

The prior art also describes various embodiments for providing alist-based subscription service, where one group of embodiments involvesreceiving a subscription to a list to which multiple list members areassociated and then providing a notification when an aggregated state ofthe list satisfies a condition. The aggregated state of the list isbased on at least a portion of the state information that pertains toeach of the list members. Another group of embodiments involves sendinga subscription to a list to which multiple list members are associatedand then receiving a notification when an aggregated state of the listsatisfies a condition. Unfortunately, as before, multiple subscriptionsare generated for multiple requests for presence information regardingthe same presentity.

In another prior art system, a presence server sets a group identifieras an identifier which is used to collectively look up a group ofmultiple pieces of presence information provided by presence informationproviders who have agreed to a use policy, aggregates and stores thepresence information under the group identifier, and delivers thepresence information requested to the group identifier. Each presentityprovides the presence server with its presence information targeted tothe group identifier. Each watcher requests the group identifier for thepresence information provided by the presentities, and receives thepresence information delivered from the presence server. However,multiple requests for presence information by group identifier stillresults in multiple subscriptions being created per presentity.

A prior art method for reducing memory usage for communications betweenservers in a communication network utilizing SIP does so by controllingestablishment of SIP-Tunnels. A single SIP-Tunnel for a certain eventpackage is utilized for multiple subscriptions between one instance of arequesting server such as a resource list server, and one instance of anapplication server such as a presence server. The SIP-Tunnel is thenutilized to send all SIP NOTIFY messages between these two entities toreduce memory usage at both ends by removing the overhead created bySIP. However, this method is silent with regard to reducing oreliminating multiple subscriptions created per presentity as isdescribed hereinbelow.

In another prior art system a presence server acts as a special SIPapplication server to manage service- and user-related presenceinformation, and employs a resource list server to allow single presencesubscriptions on a group of entities that results in an aggregatednotification with the requested data. Unfortunately, here too aremultiple subscriptions generated for multiple requests for presenceinformation regarding the same presentity.

Prior art mechanisms that do describe reducing the number ofsubscriptions between a resource list server and a presence server donot describe how to handle subscriptions for watcher information.

Systems, methods, and/or computer program products for reducing thenumber of presence server subscriptions generated by a resource listserver for watcher subscriptions to resource lists, as well as handlesubscriptions for watcher information, would therefore be advantageous.

SUMMARY OF THE INVENTION

In one aspect of the invention a method is provided for optimizedcooperation between resource list servers and presence servers, themethod including receiving a subscription request from a watcher, wherethe subscription request identifies a resource list and is a request toreceive presence information regarding each of a plurality ofpresentities listed on the resource list, and generating a subscriptionrequest to a presence server for presence information regarding anypresentity listed on the resource list only if no other currently-activesubscription request is known by the resource list server to exist forpresence information regarding the presentity. In other aspects of theinvention the method may be implemented in computer hardware as a systemand/or in computer software in a computer program product including acomputer readable medium and computer program instructions stored on thecomputer readable medium, operative to cause the computer to perform thefunctions and operations associated with the above-disclosed method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be understood and appreciated more fully from thefollowing detailed description taken in conjunction with the appendeddrawings in which:

FIG. 1 is a simplified conceptual illustration of a system for optimizedcooperation between resource list servers and presence servers,constructed and operative in accordance with an embodiment of theinvention;

FIGS. 2A and 2B, taken together, is a simplified flowchart illustrationof an exemplary method of operation of the system of FIG. 1, operativein accordance with embodiments of the invention;

FIG. 3 is a simplified conceptual illustration of an alternative systemfor optimized cooperation between resource list servers and presenceservers, constructed and operative in accordance with an embodiment ofthe invention;

FIG. 4 is a simplified flowchart illustration of an exemplary method ofoperation of the system of FIG. 3, operative in accordance withembodiments of the invention; and

FIG. 5 is a simplified block diagram illustration of an exemplaryhardware implementation of a computing system, constructed and operativein accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is now described within the context of one or moreembodiments, although the description is intended to be illustrative ofthe invention as a whole, and is not to be construed as limiting theinvention to the embodiments shown. It is appreciated that variousmodifications may occur to those skilled in the art that, while notspecifically shown herein, are nevertheless within the true spirit andscope of the invention.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Reference is now made to FIG. 1, which is a simplified conceptualillustration of a system for optimized cooperation between resource listservers and presence servers, constructed and operative in accordancewith an embodiment of the invention. In the system of FIG. 1, a resourcelist server (RLS) 100 manages or otherwise accesses one or more resourcelists 102, where each resource list 102 includes identifiers for one ormore presentities. RLS 100 receives subscription requests from one ormore watchers, where each subscription request indicates one of resourcelists 102, and is a request to receive presence information for eachpresentity listed on the indicated resource list 102. RLS 100 preferablymaintains a record of each subscription request received from a watcher,indicating the identity of the watcher and of the resource list 102indicated in the subscription request. For each presentity included inthe resource list indicated in a subscription request received from awatcher, RLS 100 generates a subscription request for presenceinformation for the presentity, and preferably does so only if there isno currently-active subscription request for presence information forthe presentity that RLS 100 previously generated or, if RLS 100 is partof a cluster of resource list servers, that any of the other servers inthe cluster generated, such as in response to a prior watchersubscription request. Subscription requests generated by RLS 100 do notidentify the watcher as the subscriber, but preferably identify RLS 100as the subscriber. RLS 100 submits, or otherwise causes to be submitted,its subscription requests to a presence server 104 that is tasked withproviding presence information for the presentity. When a notificationof presentity presence information is received from a presence server,RLS 100 preferably stores the presence information in a presenceinformation database 106. For each presentity included in the resourcelist indicated in a subscription request received from a watcher, RLS100 provides the watcher with presence information regarding thepresentity. Preferably, RLS 100 only provides presence information whenpresence information for all of the presentities in the resource list isreceived, whereupon RLS 100 consolidates the presence information of allthe presentities and provides the consolidated presence information tothe watcher. When providing a watcher with presence information, RLS 100preferably applies presence rules filtering in accordance withconventional techniques, and provides presence information in the formof a resource list meta-information (RLMI) document.

The system of FIG. 1 may be illustrated by way of example within thecontext of the IBM WebSphere® XML Document Management Server (XDMS) andIBM WebSphere® Presence server, commercially available fromInternational Business Machines, Inc., Armonk, N.Y. In this context,when an RLS, such as in an RLS cluster, receives a subscription requestfrom a watcher indicating a resource list, it interacts with the sharedlist XDMS to receive the indicated resource list and the identity of itsmember presentities. For each resource list member the RLS creates abackend subscription via an IP Multimedia Subsystem (IMS) core entrypoint Call Session Control Function (CSCF). Each subscription to aresource is routed to the correct home network and then, via the routingcomponent, to the correct presence server or presence server cluster.Regardless of the number of subscriptions to the same resource list orto different resource lists that are managed by the RLS or RLS cluster,only one subscription is made by the RLS or RLS cluster for presenceinformation for any given presentity. Where RLSs cooperate in a cluster,cluster-level synchronization is preferably employed to ensure that onlyone RLS server in the cluster creates a subscription for presenceinformation for a given presentity. An RLS subscription for presenceinformation for a given presentity preferably remains active as long asthere is at least one RLS in the RLS cluster managing an activesubscription to a resource list that includes the presentity.

Reference is now made to FIGS. 2A and 2B, which, taken together, is asimplified flowchart illustration of an exemplary method of operation ofthe system of FIG. 1, operative in accordance with embodiments of theinvention. In the method of FIGS. 2A and 2B a subscription request isreceived from one or more watchers, where each subscription requestindicates a resource list and is a request to receive presenceinformation for each presentity listed on the indicated resource list(step 200). For each presentity included in the resource list indicatedin a subscription request received from a watcher, a subscriptionrequest is generated for presence information for the presentity (step202), preferably only if there is no currently-active subscriptionrequest for presence information for the presentity (step 203), andwithout identifying the watcher as the subscriber. Each generatedsubscription request is submitted to a presence server that is taskedwith providing presence information for the presentity (step 204).Notifications of presence information for the presentities on theresource list are received from the presence servers that manage thegenerated subscriptions (step 206), and are provided to the watcher(step 208), preferably where all of the presence information for all ofthe presentities on the resource list is provided in a consolidatedformat.

One consequence of implementing the system and method of FIGS. 1, 2A,and 2B, is that presence server 104 does not know which watchers havesubscribed to which resource lists, and thus to their underlyingpresentities. As such, presence server 104 is not able to provide tointerested parties information regarding these watchers and thepresentities about which these watchers receive presence information.One remedy for this is now described with reference to FIGS. 3 and 4.

Reference is now made to FIG. 3, which is a simplified conceptualillustration of an alternative system for optimized cooperation betweenresource list servers and presence servers, constructed and operative inaccordance with an embodiment of the invention. The system of FIG. 3 issubstantially similar to the system of FIG. 1 with the notable exceptionthat RLS 100 provides watcher information to presence server 104 via aPUBLISH operation that is performed whenever a new subscription requestis received from a watcher to resource list handled by RLS 100 andwhenever the state of a subscription to a resource list changes. Thewatcher information provided by RLS 100 via a PUBLISH operationpreferably includes details such as the subscriber ID, the subscriptionID, the subscription state, and the event that caused the state change(e.g., subscription timed out). Presence server 104 stores watcherinformation in a watcher information database 300, and when presenceserver 104 receives a PUBLISH request from RLS 100 with watcherinformation, presence server 104 stores the information in database 300,preferably searching database 300 for any information it may alreadyhave for the watcher and updating the information accordingly. In thisway, presence server 104 will be able to accept subscriptions forwatcher information and thereafter provide watcher information to suchsubscribers.

As was mentioned above, subscription requests generated by RLS 100 donot identify the watcher as the subscriber, but preferably identify RLS100 as the subscriber. In order to prevent presence server 104 frommaintaining watcher information in database 300 where RLS 100 is listedas the watcher, presence server preferably maintains a list 302 of RLSidentities. If a subscription request is received by presence server104, and the identity of the subscriber as indicated by the subscriptionrequest matches an RLS identity found in list 302, presence server neednot maintain watcher information in database 300 for the subscriber.

Reference is now made to FIG. 4, which is a simplified flowchartillustration of an exemplary method of operation of the system of FIG.3, operative in accordance with embodiments of the invention. In themethod of FIG. 4, whenever the RLS receives a new subscription requestfrom a watcher to a resource list and whenever the state of asubscription to a resource list changes (step 400) an RLS sends watcherinformation to a presence server via a PUBLISH operation (step 402). Thepresence server that receives the watcher information stores thereceived watcher information as new information regarding the watcher oras an update to any information it already has regarding the watcher(step 404).

Referring now to FIG. 5, block diagram 500 illustrates an exemplaryhardware implementation of a computing system in accordance with whichone or more components/methodologies of the invention (e.g.,components/methodologies described in the context of FIGS. 1-4) may beimplemented, according to an embodiment of the invention.

As shown, the techniques for controlling access to at least one resourcemay be implemented in accordance with a processor 510, a memory 512, I/Odevices 514, and a network interface 516, coupled via a computer bus 518or alternate connection arrangement.

It is to be appreciated that the term “processor” as used herein isintended to include any processing device, such as, for example, onethat includes a CPU (central processing unit) and/or other processingcircuitry. It is also to be understood that the term “processor” mayrefer to more than one processing device and that various elementsassociated with a processing device may be shared by other processingdevices.

The term “memory” as used herein is intended to include memoryassociated with a processor or CPU, such as, for example, RAM, ROM, afixed memory device (e.g., hard drive), a removable memory device (e.g.,diskette), flash memory, etc. Such memory may be considered a computerreadable storage medium.

In addition, the phrase “input/output devices” or “I/O devices” as usedherein is intended to include, for example, one or more input devices(e.g., keyboard, mouse, scanner, etc.) for entering data to theprocessing unit, and/or one or more output devices (e.g., speaker,display, printer, etc.) for presenting results associated with theprocessing unit.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

While the methods and apparatus herein may or may not have beendescribed with reference to specific computer hardware or software, itis appreciated that the methods and apparatus described herein may bereadily implemented in computer hardware or software using conventionaltechniques.

While the invention has been described with reference to one or morespecific embodiments, the description is intended to be illustrative ofthe invention as a whole and is not to be construed as limiting theinvention to the embodiments shown. It is appreciated that variousmodifications may occur to those skilled in the art that, while notspecifically shown herein, are nevertheless within the true spirit andscope of the invention.

What is claimed is:
 1. A system comprising: a first processing systemincluding at least one processor device configured to: receive asubscription request that identifies a list indicating a plurality ofnetwork entities and includes a request for information for one or morenetwork entities within said list; determine active subscriptionrequests for individual network entities and compare individual networkentities of said list to said determined active subscription requests;receive information pertaining to individual network entities of saidlist from a second processing system in response to said comparisonindicating said active subscription requests for those individualnetwork entities; and generate one or more subscription requests eachfor a corresponding one of said network entities of said list andrequesting information pertaining to that network entity from saidsecond processing system, wherein each subscription request is generatedfor said corresponding network entity in response to no othercurrently-active subscription request being determined by said firstprocessing system to exist for said information pertaining to thatnetwork entity.
 2. The system of claim 1, wherein said first processingsystem includes a resource list server, said second processing systemincludes a presence server, and said requested information includespresence information.
 3. The system of claim 2, wherein said resourcelist server is configured to generate said subscription requests,wherein each of said generated subscription requests includes a requestto receive presence information pertaining to said corresponding networkentity.
 4. The system of claim 3, wherein said resource list server isconfigured to cause said generated subscription requests to be submittedto at least one presence server that provides presence informationregarding said corresponding network entities.
 5. The system of claim 4,wherein said resource list server is configured to receive presenceinformation regarding one or more of said network entities listed onsaid list, and provide said received presence information to a requesterof said presence information.
 6. The system of claim 2, wherein saidresource list server is configured to generate a subscription requestidentifying said resource list server as a subscriber of said generatedsubscription request.
 7. The system of claim 2, wherein said resourcelist server is configured to provide information regarding a requesterof said presence information to said presence server.
 8. The system ofclaim 7, wherein said resource list server is configured to provide saidinformation pertaining to said requester in response to a change to astate of a subscription to said list.
 9. The system of claim 7, whereinsaid presence server is configured to maintain a list of resource listserver identities, and refrain from maintaining requester informationfor a subscriber in response to an identity of said subscriber matchingan identity of a resource list server.
 10. A method comprising:receiving a subscription request at a first processing system thatidentifies a list indicating a plurality of network entities andincludes a request for information for one or more network entitieswithin said list; determining at said first processing system activesubscription requests for individual network entities and comparingindividual network entities of said list to said determined activesubscription requests; receiving at said first processing systeminformation pertaining to individual network entities of said list froma second processing system in response to said comparison indicatingsaid active subscription requests for those individual network entities;and generating at said first processing system one or more subscriptionrequests each for a corresponding one of said network entities of saidlist and requesting information pertaining to that network entity fromsaid second processing system, wherein each subscription request isgenerated for said corresponding network entity in response to no othercurrently-active subscription request being determined by said firstprocessing system to exist for said information pertaining to thatnetwork entity.
 11. The method of claim 10, wherein said firstprocessing system includes a resource list server, said secondprocessing system includes a presence server, and said requestedinformation includes presence information.
 12. The method of claim 11,wherein each of said generated subscription requests includes a requestto receive presence information pertaining to said corresponding networkentity.
 13. The method of claim 12, further comprising: submitting saidgenerated subscription requests to at least one presence server thatprovides presence information pertaining to said corresponding networkentities.
 14. The method of claim 13, further comprising: receivingpresence information pertaining to one or more of said network entitieslisted on said list; and providing said received presence information toa requester of said presence information.
 15. The method according toclaim 11, wherein said generating comprises: generating a subscriptionrequest indicating a resource list server as a subscriber of saidgenerated subscription request.
 16. The method of claim 11, furthercomprising: providing information pertaining to a requester of saidpresence information to said presence server.
 17. The method of claim16, wherein said providing information comprises: providing saidinformation pertaining to said requester in response to a change to astate of a subscription to said list.
 18. The method of claim 16,further comprising: maintaining a list of resource list serveridentities at said presence server; and refraining from maintaining atsaid presence server requester information for a subscriber in responseto an identity of said subscriber matching an identity of a resourcelist server.
 19. A computer program product comprising: a computerreadable storage medium that excludes a computer readable signal mediumand includes computer program instructions stored thereon and configuredto: receive a subscription request at a first processing systemidentifying a list and including a request to receive informationpertaining to one or more network entities listed on said list;determine at said first processing system active subscription requestsfor individual network entities and compare individual network entitiesof said list to said determined active subscription requests; receive atsaid first processing system information pertaining to individualnetwork entities of said list from a second processing system inresponse to said comparison indicating said active subscription requestsfor those individual network entities; and generate at said firstprocessing system one or more subscription requests each for acorresponding one of said network entities of said list and requestinginformation pertaining to that network entity from said secondprocessing system, wherein each subscription request is generated forsaid corresponding network entity in response to no othercurrently-active subscription request being determined by said firstprocessing system to exist for information pertaining to that networkentity.
 20. The computer program product of claim 19, wherein said firstprocessing system includes a resource list server, said secondprocessing system includes a presence server, and said requestedinformation includes presence information.
 21. The computer programproduct of claim 20, wherein each of said generated subscriptionrequests includes a request to receive presence information pertainingto said corresponding network entity.
 22. The computer program productof claim 21, wherein said computer program instructions are furtherconfigured to: submit said generated subscription requests to at leastone presence server that provides presence information pertaining tosaid corresponding network entities.
 23. The computer program product ofclaim 22, wherein said computer program instructions are furtherconfigured to: receive presence information pertaining to one or more ofsaid network entities listed on said list; and provide said receivedpresence information to a requester of said presence information. 24.The computer program product of claim 20, wherein said computer programinstructions are further configured to: generate a subscription requestindicating a resource list server as a subscriber of said generatedsubscription request.
 25. The computer program product of claim 20,wherein said computer program instructions are further configured to:provide information pertaining to a requester of said presenceinformation to said presence server.
 26. The computer program product ofclaim 25, wherein said computer program instructions are furtherconfigured to: provide said information pertaining to said requester inresponse to a change of a state of a subscription to said list.
 27. Thecomputer program product of claim 25, wherein said computer programinstructions are further configured to: maintain a list of resource listserver identities at said presence server; and refrain from maintainingrequester information pertaining to a subscriber in response to anidentity of said subscriber matching an identity of a resource listserver.